There is an engine of the type having a supercharger provided therein (which supercharger is also referred to as a "turbocharger" or simply called a "turbo"). The supercharger causes exhaust gases from the engine to rotate a turbine. Then, a compressor, which is coaxially aligned with the turbine, supplies intake air under pressure to the engine.
The engine is provided with a main cooling system and a sub-cooling system. The former system cools the engine, while the latter does, e.g., the supercharger. The sub-cooling system is positioned alongside the main cooling system.
One example of a cooling system for the above engine with the supercharger is disclosed in published Japanese Examined Patent Application No. 2-52091. The cooling system for an internal combustion engine with a turbocharger can cool a bearing portion, even after the engine is deactivated. In addition, the cooling system has an increased amount of freedom in positioning of the turbocharger. Further, the cooling system facilitates replenishment of cooling water to an engine cooling system. Moreover, the cooling system is designed to promote the warm-up of the turbocharger, and further to reduce a load on a cooling pump.
Another example is disclosed in published Japanese Examined Patent Application No. 6-3143. A cooling system for an internal combustion engine with a turbocharger includes an engine cooling water-circulating circuit and a turbocharger cooling water-circulating circuit. The former circuit is formed between a water pump for the engine, a water jacket formed in the engine, and a radiator, while the latter circuit is formed between a water jacket for the turbocharger, a water-filling tank, and a water pump. The water jacket for the turbocharger is branched off from the above engine water jacket in communication therewith. The water-filling tank is positioned higher than the turbocharger. The water-filling tank has a water level set higher than a degassing portion of the radiator at an upper portion thereof. The cooling system is characterized by: an air chamber positioned in the water-filling tank at an upper portion thereof, the air chamber being communicated to a distal end of a cooling water outlet pipe, the cooling water outlet pipe being connected to a cooling water outlet of the above turbocharger water jacket, a cooling water return pipe, through which the aforesaid cooling water outlet and the intake side of the water pump are communicated to one another at the bottom of the tank, the cooling water outlet being open below the water level of the tank, a one-way valve designed to open only in an internal tank direction, the one-way valve being provided at an outlet opening of a degassing passage, the outlet opening being open above the water level of the tank, and a degassing pipe connected to a degassing portion of the radiator at the top portion thereof, the degassing pipe being communicated to the degassing passage through the one-way valve. This invention provides smooth movements of steam that are generated in the water jacket for the turbocharger during engine stop, and further permits the generated steam to promote circulation of the cooling water in the turbocharger cooling water-circulating circuit.
A further example is disclosed in published Japanese Examined Model Utility Application No. 8-2434. In a cooling system for a supercharger for use on an internal combustion engine, a housing covering a bearing portion of the supercharger is positioned higher than a liquid level of cooling water in a radiator. The cooling water is introduced into a cooling water passage in the housing, thereby cooling the bearing portion. The cooling system is characterized by: a cooling water supply passage, through which the cooling water passage in the housing is communicated to either the discharge side of a water pump or a cylinder block; a return passage through which the cooling water passage is communicated to either the intake side of the water pump or the radiator; a reservoir tank for use on the supercharger, which tank is communicated to a cooling water passage in the supercharger, the reservoir tank being positioned higher than the housing, the above supercharger reservoir tank and a reservoir tank for use on the radiator being communicated to one another through a cap for use on the supercharger; a valve for releasing pressure in the supercharger reservoir tank to the above radiator reservoir tank when the internal pressure of the supercharger reservoir tank exceeds a predetermined value, the valve being provided on the above supercharger cap; a valve for introducing cooling water into the supercharger reservoir tank from the radiator reservoir tank when the internal pressure of the supercharger reservoir tank falls below the predetermined value, the valve being provided on the supercharger cap. This invention can introduce the cooling water into the housing, thereby providing an improved cooling efficiency, even when the housing for the supercharger is positioned higher than the liquid level of the cooling water in the radiator.
A yet further example is disclosed in published Japanese Unexamined Model Utility Application No. 6-76622. In a cooling system for a supercharger for use on an internal combustion engine as disclosed in this publication, a center housing covering a journal portion of the supercharger is positioned higher than a water level of cooling water in a radiator. Some cooling water circulating in an engine cooling water circulation system is introduced into a cooling water passage in the center housing, thereby cooling the journal portion. The radiator is disposed substantially midway along the engine cooling water circulation system. A reservoir tank communicated to the cooling water passage in the center housing is positioned higher than the center housing. The reservoir tank is communicated to the radiator through a pressurization cap. The reservoir tank is communicated to an inlet port of a water pump in the engine cooling water circulation system. The pressurization cap is provided with a valve that is opened for releasing the inner pressure of the reservoir tank to the radiator when the internal pressure of the reservoir tank is greater than a predetermined pressure. The cooling system is characterized in that the valve of the pressurization cap has a valve opening pressure set to be 0.7 kg/cm2 or less. This invention controls a rise in temperature inside the center housing of the supercharger immediately after the engine is deactivated.
Other cooling systems for an engine having a supercharger incorporated therein are disclosed in published Japanese Unexamined Utility Model Applications 6-37531 and 7-4841.
In conventional cooling systems for an engine with a supercharger, there is one system of the type as illustrated in FIGS. 11 and 12. That is, a single hose 126 connects a thermocase 118 and a supercharger 112 in communication with one another. The thermocase 118 is attached to a cylinder head 106 of an engine 102. Cooling water flows from the thermocase 118 toward the supercharger 112 as shown by the arrows in FIG. 12.
As seen from FIG. 11, the hose 126 is positioned in front of an exhaust manifold 114. This layout has advantages in that the piping can be laid at the shortest distance, and further that there exists no substantial difference in height between the hose 126 and the exhaust manifold 114. However, in this layout, such piping presupposes the absence of any obstacle in front of the exhaust manifold 114.
In fact, an obstacle is usually present in front of the exhaust manifold 114, and the hose 126 cannot be placed in front of the exhaust manifold 114. Therefore, there has been a continuing desire for an improved method.
By way of a countermeasure to obviate the aforesaid inconvenience, a hose 226 (FIGS. 13 and 14) has an intermediate pipe 242 incorporated therein and located substantially midway along the hose 226. The hose 226 intercommunicates a thermocase 218 and a supercharger 212. The thermocase 218 is fitted to a cylinder head 206 of an engine 202.
As illustrated in FIGS. 13 and 14, in this piping structure, the intermediate pipe 242 bypasses an exhaust manifold 214, and is instead laid through an upper portion of the exhaust manifold 214. A bracket supports the intermediate pipe 242 onto the cylinder head cover. Cooling water flows from the thermocase 218 toward the supercharger 212 as shown by the arrows in FIG. 14.
In this case, however, there are differences in height along the piping. As a result, air (steam) is generated in the supercharger 212 at an engine-soaking period, and is then lodged in the intermediate pipe 242.
Such stagnant air (steam) causes airlock in a sub-cooling system for use on a supercharger. The occurrence of the airlock fails to feed sufficient cooling water into the supercharger, with consequential seizure of the supercharger.